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SOME PETROLOGICAL APPLICATIONS
Geochemical thermometry of marginal rocks from the Skaergaard intrusion Modeling the formation of ferrodiorites from the Chazhma sill, Kamchatka Modeling polybaric fractionation of MORB glasses from Mid-Atlantic Ridge Modeling the generation of high-Al basalts from the Klyuchevskoy volcano, Kamchatka
UT-04: UT-08: EC-10: MEO-18: KT-47: EG4507: Ol (1443oC) Aug (1233oC) Pl (1174oC), Pl (1332oC) Ol (1231oC) Aug (1164oC), Ol (1385oC) Aug (1199oC) Pl (1187oC), Pl + Ol (1248 oC) Aug (1161oC), Ol (1346oC) Pl (1191oC) Aug (1189oC), Pl (1242oC) Ol (1225oC) Aug (1163oC).

1150
WM

Tem p ,°C

1100 1050 1000 15 -12 -11 -10

NN O

A

1150 1100 1050 1000
COMAGMAT modeling

B

Fractional Equilibrium

-9

-8

-7

-6

F eO, wt%

Leucocratic rocks Pl-diabases

C

15

50

55
Ol+Pl

60

65

70

D
Pl +C px +M t

10

10

5 -12 -11 -10 -9 -8

5

log fO2

-7

-6

50

55

60

SiO2, wt%

65

70


METHOD OF GEOCHEMICAL THERMOMETRY
Samples of Ol-Pl cumulates
Rock 1 (enriched with Ol)
INTERSECTION OF MODELED LIQUID LINES OF DESCENT

Rock 1 Temperature Rock 2
Same liquid composition

Same intercumulus

Rock 2 (enriched with Pl)

MgO in the melt

The method was designed to extract genetic information as "recorded" in the whole chemistry of cumulus rocks, such as the temperature, intercumulus melt and mineral compositions, and the initial modal (i.e. phase) proportions.

Method of geochemical thermometry is accomplished by means of computer modeling of the course of equilibrium crystallization for a set of rocks that assumed to have contained the same intercumulus liquid composition.


GEOCHEMICAL THERMOMETRY OF MARGINAL ROCKS from the Skaergaard intrusion
COMPOSITIONS OF THE MARGINAL ROCKS Components SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O P2O5 Primitive cumulates [Hoover, 1989]
UT-04, d=2.5 UT-08, d=8.5 EC-10, d=1.0 MEO-10, d=3.0 KT-47, d=6.0

Chilled gabbro
EG4507, n.d.

44.65 0.69 4.88 14.16 0.24 23.61 9.15 0.81 0.03 0.00

48.38 0.60 20.91 7.19 0.10 7.06 11.79 2.61 0.17 0.03

46.92 0.63 9.36 12.84 0.10 17.22 11.14 1.22 0.04 0.02

47.45 0.40 18.32 9.49 0.15 9.83 10.40 2.36 0.06 0.00

48.19 0.81 11.37 11.04 0.19 14.53 11.60 1.78 0.13 0.08

48.08 1.17 17.22 9.63 0.16 8.62 11.38 2.37 0.25 0.10

These rocks belong to the Marginal Border Series of the Skaergaard intrusion. All of them were selected within 10 m from the intrusive contact and have no any record of parental magma fractionation. The results indicate a wide high-temperature field of Ol for high-magnesia samples and an early crystallization of Pl for aluminum enriched compositions.

UT-04: UT-08: EC-10: MEO-18: KT-47: EG4507:

Ol (1443oC) Aug (1233oC) Pl (1174oC), Pl (1332oC) Ol (1231oC) Aug (1164oC), Ol (1385oC) Aug (1199oC) Pl (1187oC), Pl + Ol (1248 oC) Aug (1161oC), Ol (1346oC) Pl (1191oC) Aug (1189oC), Pl (1242oC) Ol (1225oC) Aug (1163oC).


The Skaergaard intrusion
In these T-X coordinates the modeled liquid lines of descent demonstrate a closing together and intersection near 1165oC. This intersection is consistent with the premise that the selected rocks were mechanical mixtures of cumulus crystals plus a trapped melt. Average liquid composition representing this cluster of six evolutionary lines at 1165oC is considered to present a probable initial melt composition intrinsic to the original crystal mush from which the contact rocks have been crystallized.

a M

p &

n e g F s n i k t a W

z i l a r d r o i j

s d e

t c e i

n o

t a
x O O i T i S

6 1
e d i 2 O

5 o % . t w C
8 6 1 . 0 5

n e t U

d n u o S s l a

n l s I m e a r K

e 's r d

n i b r o F

N O Z R E P U

e F A

O l 3 O 2

4 3 5 9 . 2 1

E S I R

N

d

r i c a G s l e

E N O Z L D I M

E

g a C n M

O

4 2 6 9 1 . 0

Y S D R E

0 r e g n a K

F d 1 m k r o i j a s g u l 2

N Z R E W O L

2 K a N

O 2

6 0 7 3 . 2 5 1 . 0 y r

r a M

e R g r o B l a n i

s u t l d i S r e

s f o ) S B M ( s

o e G

A L

c m e h E Y A L

i R S N E D I H a c

I S E

e h T l

2 P

o m r

t e m
5 O

5 0 4 1 o

e t a r p m

C , e r u

3 0 2 1

6 1

5 C °

0 5 1 0 1 4

5 4 0

i S 0 5

0 6 2 O

6 4 2

2 O i T 0 1 8

5 0

A 2 5 0 1

5 3 O l 5 2 0

5 0 1

e F 3 5 0 2

T

o 4 0 3 1

O C i B c v o H M e p x E

a N & y 8 9 1 , T A M G n e m i r

s 9 1 , d n u e o d l a t m

r p m e T

C , e r u t a

0 2 1

6 1

5 C °

7 0 5 4 G E m a s r e h t O

s e l p

0 1

1 5 0

M 0 2 5 1

O g 0 5 2

1 5 0

O a C 5 0 2

1 0

2 N 4 3

O 2 a 5


Cape Kronotsky

Taking tea among layered diabases of the Chazhma sill (Eastern Kamchatka, 1982)


MODELING THE FORMATION OF FERRODIORITES from the Chazhma sill, Kamchatka
This intrusion is composed of differentiated rocks ranging from high-Al diabases to diorites and granophyres. The diorites make up a large number of fine-grained leucocratic layers embedded between massive more dark diabases.

These observations allowed us to conclude that there were no large scale mixing between these two magmas. This leucocratic material was probably injected into the main magma body simultaneously with, or just after emplacement, as the body began to crystallize.


MODELING THE FORMATION OF FERRODIORITES from the Chazhma sill, Kamchatka
Geochemical studies have demonstrated that the compositions of Chazhma layers display a trend of decreasing iron with increasing silica content. The presence of Magn crystals indicates these trends were originated due to the fractionation of magnetite-bearing assemblages from same basaltic andesite parent.
1150
WM

Te m p ,°C

1100 1050 1000 15

NN O

A

1150 1100 1050 1000
COMAGMAT modeling

B

Fractional Equilibrium

-12 -11 -10 -9
Leucocratic rocks Pl-diabases

-8

-7

-6

50 15

55
Ol+Pl

60

65

70

C

D
Pl +C px +M t

Fe O , w t%

10

10

5 -12 -11 -10 -9 -8 -7 -6

5 50 55 60 65 70

log fO2

SiO2, wt%

Finally, simulations near NNO buffer were carried out to accurately reproduce the iron-silica relations observed in the Chazhma suite.


MODELING POLYBARIC FRACTIONATION OF MORB GLASSES
The tholeiitic compositions form two evident clusters that could indicate of two different tholeiitic magmas fractionating Cpx at a depth. In attempt to understand this diversity, we carried out a set of polybaric calculations simulating fractionation at low to elevated pressures for a proposed highmagnesia parental basalt. The results evidence for the diversity of tholeiitic glasses has been derived from same precursor, with these two compositional groups being different in the depth of the fractionation process. A part of these melts has been originated near 6 kbars, whereas the majority of the glasses indicate of low pressures crystallization at the depth of 2-3 kbars.


KLYUCHEVSKOY'S GROUP OF VOLCANOES (Kamchatka, Russia)

Klyuchevskoy: basalts Kamen: basaltic andesites Bezymianny: andesites


MODELING THE GENERATION OF HIGH-AL BASALTS from the Klyuchevskoy volcano, Kamchatka
Al2O3, wt%
20

High-Al basalts
18

16

14

High-Mg basalts
12 4 6 8 10

MgO, wt%

The volcanic edifice consists of numerous basalt lava sheets and pyroclastic materials, ranging continuously from high-Mg basalts to high-Al basalts containing at least 18% Al2O3. The proposed genetic link between highmagnesia and high-alumina basalts includes the removal of mafic phases, principally olivine and augite.


MODELING OF THE THE ISOBARIC FRACTIONATION PROCESS at unhydrous conditions ranging from 1 atm to 20 kbars
At the pressures more than 8 kbars equilibrium crystallization of the highmagnesia parent results in the alumina enriched liquids. However, the modeled trends do not provide an adequate match with the observed CaO-MgO trend. A possible explanation of these discrepancies is to link the formation of the observed suite with decompression fractionation of the parental highmagnesia magma containing small but significant water.

22 20
12 kbar

Klyuchevskoy lavas High-Mg basalt
16 kbar 20 kbar

3

Al2 O

18 16 14 12

8 kbar 4 kbar 1 atm

4 12

6

8

10

12

CaO, wt.%

10
1 atm

8 6 4 4 6
12 kbar 20 kbar

COMAGMAT model

8

10

12

MgO, wt%


THE OPTIMAL MODEL OF THE DECOMPRESSION FRACTIONATION for the high-Mg magma of the Klyuchevskoy volcano
These chemical trends can be produced by ~40% fractionation of the Ol-Aug-Sp-Opx assemblage during ascent of the magma over the pressure range 19-7 kbars. This is consistent with the decrease in the temperature from 1350 to 1100oC, with ~2 wt.% of H2O in the initial melt.


PROPOSED EVOLUTION OF THE MAGMA PLUMBING SYSTEM for the Klyuchevskoy volcano

0 10 20 FRACTIONATION

Eruptive activity
Degassing and abundant plagioclase crystallization MAGMA M IXING

Magma temp,°C
1100 1150 1200 1250 1300 1350

Depth, km

- 79.0

- 77.3

- 82.0

- 69.6

30 40 50 60 70

Pl
- 83.9 - 82.9 - 85.3

18.0 17.3 16.6 15.9 15.4 14.8 14.4 13.9

5.5 6.3 7.1 8.1 8.7 9.5 10.4 11.6

2.9 2.7 2.5 2.4 2.3 2.2 2.1 2.0 H O,%

35 30 25 20 15 10 5 0

- 87.3

- 86.7

- 87.8

Opx Ol
- 90.0 - 90.3 - 89.6

Cpx

Sp

Al 2O 3 MgO

,%

Crystallization sequence

Melt composition


CONVECTIVE-CUMULATIVE MODEL SIMULATING THE FORMATION OF DIFFERENTIATED SILLS FROM THE SIBERIAN PLATFORM

Crystal settling from convecting magma


DEVELOPMENT OF "INTRUSION" PROGRAM AND FIELD STUDIES

Integration of physical constraints into the COMAGMAT model


Thickness, meters

COMPARISON OF COMPARISON CALCULATIONS WITH OBSERVATIONS

Natural data for the Vavacan sill
Ni Cr V Ba

Calculations




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